Level-3 daily merged Copernicus-GlobColour multi-sensor Remote Sensing Reflectance (Rrs(λ)) from the Copernicus Marine Environmental Monitoring Service (CMEMS) is used as data source. The aCDOM(443) was estimated using the gsmA parametrizations for the southern Beaufort Sea (Matsuoka et al., 2013) with some modifications; while DOC was retrieved using an empirical aCDOM(443)-DOC relationship developed by Juhls et al. (2022), valid across the fluvial-marine transition zone of the Mackenzie River–Beaufort Sea region, Level-4 daily maps of aCDOM(443) and DOC for the Mackenzie River-Beaufort Sea region (122-142ºW and 68-73ºN) are distributed in the regular latitude–longitude grid at a spatial resolution of 4 km. The data is available from 1st January 2002 to 31st October 2023. Additionally, 8-day means, and monthly mean data are also provided. The dataset consists of four variables:
(i) Chromophoric Dissolved Organic Matter at 443 nm (aCDOM(443) [m-1])
(ii) Dissolved Organic Carbon (DOC [µM])
(iii) water type mask (coastal/oceanic)
(iv) model relative error for Rrs(443) (∆Rrs(443) [%])
(v) aCDOM(443) uncertainty (σaCDOM [m-1])
(vi) DOC uncertainty (σDOC [µM]), YYYYMMDD_aCDOM443_DOC_l4_4km_P1D.nc (This dataset contains daily Level-4 aCDOM and DOC product from satellite observations for the Mackenzie River-Beaufort Sea region)
YYYYMMDD_YYYYMMDD_aCDOM443_DOC_l4_4km_P8D.nc (This dataset contains daily Level-4 aCDOM and DOC product from satellite observations for the Mackenzie River-Beaufort Sea region)
YYYYMMDD_YYYYMMDD_aCDOM443_DOC_l4_4km_P1M.nc (This dataset contains monthly Level-4 aCDOM and DOC product from satellite observations for the Mackenzie River-Beaufort Sea region), In the regime-shifting Arctic, organic carbon export from river watersheds is expected to increase due to changes in hydrological regimes and permafrost thawing. Given the impact these changes have on the biogeochemical cycles of coastal and shelf areas, robust monitoring of major Arctic rivers is needed. During ice-free season, ocean color remote sensing has shown to be an effective monitoring tool for remote, under-sampled areas with limited access such as the Beaufort Sea region. It offers synoptic spatio-temporal coverage, filling in the gaps among the scarce in situ data and improving our knowledge of land-to-ocean transport pathways and coastal ocean dynamics near riverine zones. Remote sensing of Chromophoric Dissolved Organic Matter (CDOM) and Dissolved Organic Carbon (DOC) has proven to be a valuable approach for assessing variations in terrestrial carbon export. However, seasonal fluctuations and diverse vegetation and soil conditions of each river watershed make it difficult to establish a single retrieval method for the entire Arctic. This complexity has led to a development of several regional algorithms, yet accessible long-term series remain a challenge. We present the first long-term satellite-derived dataset quantifying the absorption coefficient of CDOM at 443 nm and DOC concentrations in the Mackenzie River–Beaufort Sea region (122–142ºW and 68–73ºN) from 1st January 1998 to 31st October 2023. We employed a modified version of the GIOP (Generalized Inherent Optical Properties) algorithm to retrieve CDOM(443) for the southern Beaufort Sea; DOC was then derived using a region-specific relationship between aCDOM(443) and DOC. The product has been validated using in situ observations from several field campaigns conducted in the area. We provide a consistent dataset that can be used to assess DOM spatial and temporal variability, trends, and export to the coastal seas, This work has been carried out as part of the ARCTIC-MON project (Advances in monitoring sea ice thickness and snow depth, ocean dynamics, and freshwater content in the Arctic using remote sensing data), funded through the Consejo Superior de Investigaciones Científicas (CSIC) (grant no. PID2021-125324OB-I00), With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Level-4 daily maps of aCDOM(443) and DOC for the Mackenzie River-Beaufort Sea region (122-142ºW and 68-73ºN) are distributed in the regular latitude–longitude grid at a spatial resolution of 4 km. The data is available from 1st January 2002 to 31st October 2023. Additionally, 8-day means, and monthly mean data are also provided. The dataset consists of four variables: (i) Chromophoric Dissolved Organic Matter at 443 nm (aCDOM(443) [m-1]) (ii) Dissolved Organic Carbon (DOC [µM]) (iii) water type mask (coastal/oceanic) (iv) model relative error for Rrs(443) (∆Rrs(443) [%]) (v) aCDOM(443) uncertainty (σaCDOM [m-1]) (vi) DOC uncertainty (σDOC [µM]), Peer reviewed

This in situ dataset collected during the ARCTIC-MON field campaign will be linked in the Barcelona Polar Lab (BPL) webpage: https://polar.icm.csic.es, The ARCTIC-MON campaign conducted at the Canadian High Arctic Research Station (CHARS) collected brightness temperatures from L-band radiometric measurements of sea ice, using the ARIEL portable L-band radiometer. This data is key to improve the emission modelling that is required for the development of the sea ice thickness products from remote sensing observations, This project is funded with the ARCTIC-MON project (PID2021-125324OB-I00) and also Programación Conjunta Internacional project called ICE-MOD, with reference PCI2019-111844-2, from the Agencia Estatal de Investigación in Spain. With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S), Brightness temperature measured over sea ice at each stop done during each days transects. Each stop is labelled within each day’s measurements, Peer reviewed

Sea ice thickness from SMOS measurements. The retrieval is based in a hybrid approach, combining the Burke emission model (Burke et al., 1979) with a machine learning algorithm. The emission model is used to generate the dataset that is then used to train a Random Forest algorithm. The sea ice thickness is retrieved only up to 1 - 1.5 m of thickness due to the limited sensitivity at the L-band. This maximum retrievable thickness is not yet included in the product but will be in the future; for safety trust values only up to 1 m, ARCTIC-MON project (PID2021-125324OB-I00), from Agencia Estatal de Investigación (AEI), This work contributes to the Institut de Ciències del Mar "Severo Ochoa Centre of Excellence" accreditation CEX2024-001494-S funded by AEI 10.13039/501100011033 of the Spanish Ministry of Science and Innovation, Daily netCDF files containing the grided sea ice thickness estimations from SMOS, Peer reviewed

Satellite observations are a key tool in this effort, employing various technologies to measure sea‑ice thickness. Altimetry satellites are sensitive to ice thicker than approximately 1 meter, while low‑frequency passive microwave sensors such as SMOS can retrieve thinner sea ice by detecting its natural microwave emission. These two approaches therefore provide complementary information. However, there is still room to improve the quality of remotely sensed sea‑ice thickness products by refining the retrieval methodologies. Progress is limited mainly by the scarcity of in situ measurements, which are essential for developing empirical models and performing robust validation.
The main objective of the project was therefore to measure sea‑ice thickness by continuously operating the SIMS instrument mounted on the icebreaker Le Commandant Charcot, and to collect in situ sea‑ice measurements during station stops. The in situ measurements were obtained through ice‑coring and drilling operations, which allowed us to validate the SIMS data and to characterize the physical properties of the sea ice. These include sea‑ice and snow thickness (measured with high precision), sea‑ice temperature, salinity, and dielectric constant—key parameters for improving the modeling required by the retrieval algorithms.
The SIMS instrument was deployed when possible given the meteorological conditions encountered when navigating through sea ice.
The figure in the attached file shows the SIMS sea ice thickness measurements during SIMSVAL project, both raw and with a median filter applied to smooth it. The stars indicate the in situ drillings done under the instrument when the ship stopped in the ice. As shown, the ground truth clearly matches the SIMS value at that point, highlighting its reliability despite the noise that appears when the ship is navigating and breaking the ice floes, We acknowledge the Spanish funding agency Agencia Estatal de Investigación (España) and Ministerio de Ciencia e Innovación (España) for its support through the ARCTIC-MON project (PID2021-125324OB-I00) that enabled us to cover travel expenses, shipping, as well as the rental and purchase of some of the required field work equipment.
We also acknowledge PONANT for providing us with berths on the icebreaker Le Commandant Charcot, for providing the SIMS and drilling instruments, and for the technical support from Daniel Cron, This work contributes to the Institut de Ciències del Mar "Severo Ochoa Centre of Excellence" accreditation CEX2024-001494-S funded by AEI 10.13039/501100011033 of the Spanish Ministry of Science and Innovation, There are three files, one for each cruise segment: - SIMSVAL: 21 March 2025 – 05 April 2025 - POLARIS: 05 April 2025 – 17 April 2025 - FANS: 17 April 2025 – 02 May 2025, Peer reviewed

Satellite observations are a key tool in this effort, employing various technologies to measure sea ice thickness. Altimetry satellites are sensitive to ice thicker than approximately 1 meter, while low-frequency passive microwave sensors such as SMOS can retrieve thinner sea ice by detecting its natural microwave emission. These two approaches therefore provide complementary information. However, there is still room to improve the quality of remotely sensed sea ice thickness products by refining the retrieval methodologies. Progress is limited mainly by the scarcity of in situ measurements, which are essential for developing empirical models and performing robust validation.

The main objective of the project was to collect brightness temperatures from L-band radiometric measurements of sea ice using the ARIEL portable L-band radiometer, and simultaneously measure sea ice thickness with the SIMS instrument, as well as sea ice conditions (salinity, temperature, and snow properties). This dataset is key to improving the emission modelling required for the development of sea ice thickness products derived from remote sensing observations, We acknowledge the Spanish funding agency Agencia Estatal de Investigación (España) and Ministerio de Ciencia e Innovación (España) for its support through the ARCTIC-MON project (PID2021-125324OB-I00) enabled us to cover travel expenses, shipping, as well as the rental and purchase of some of the required equipment.
We also acknowledge PONANT for providing us with berths on the icebreaker Le Commandant Charcot, for providing the SIMS and drilling instruments, and for the technical support from Daniel Cron, This work contributes to the Institut de Ciències del Mar "Severo Ochoa Centre of Excellence" accreditation CEX2024-001494-S funded by AEI 10.13039/501100011033 of the Spanish Ministry of Science and Innovation, There are three files, one for each cruise segment: - SIMSVAL: 21 March 2025 – 05 April 2025 - POLARIS: 05 April 2025 – 17 April 2025 - FANS: 17 April 2025 – 02 May 2025, Peer reviewed